Neutral Aun clusters

In this subsection we investigate the adsorption of O2 molecules on neutral Aun clusters with 5cluster substrate, which is chosen among the equilibrium structures of pure An clusters obtained in a previous work . We do not consider initial configurations with two separated O atoms. Thus, O2 dissociative adsorption is obtained only when that process occurs without any barrier. 

With respect to CO adsorption on neutral Aun clusters, our preliminary results show differences with previous calculations using cluster geometries extracted from the fee gold crystal. The adsorption energy of CO is minimum for the planar magic cluster Aue and shows maxima for the odd electron clusters Au5 and Au7, both with the CO absorbed on a bridge position, but the even-odd effect is not obtained for sizes larger than n=7. 

The interaction of 02 and CO with neutral Aun clusters with n = 5-10 has been recently explored in DFT calculations by Fernandez et al.160 The 02 adsorption energy exhibits odd-even effects. CO prefers to bind on the least coordinated Au atom except for n = 5 and 7.160... 

Phala et al. used DFT to probe H and CO adsorption on neutral Aun clusters with n = 1-13.162 3D clusters were used for n > 6. One interesting result from this work was the observation that the adsorption energy of H on Au6 on which CO was already adsorbed was 29 kJ/mol smaller than the H adsorption energy on the bare cluster. 

Table 4. The Coulomb-type interaction of the charge remaining on the ion at its optimum position with the charges in the cluster, when the ion is adsorbed at the hollow site (t/,oi) and with the charges in the neutral Aun cluster (f/o). The dilference between the two quantities, U, is an indication of the interaction resulting from charge transfer from the ion to the cluster and the polarization of the eluster by the negative charge of the ion. All energies are given in kJ moC. ...

Recent GGA first principles pseudopotential calculations conclude that Aun clusters adopt planar structures up to larger sizes than silver and copper, particularly the anionic species, due to relativistic effects. Specifically, Fernandez and coworkers obtain planar structures for the ground state of anionic v=l), neutral v=0), and cationic (z/=+l) species of Au(( clusters... 

Franceschetti et al. used DFT to examine interactions of 02 with Aun and Aun for n = 3-6.161 They concluded that chemisorbed states where the two O atoms where spatially separated (i.e. 02 was dissociated) were in general more stable than configurations with molecularly adsorbed 02> and that 02 binds more strongly to anionic clusters than to neutral clusters. 

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